Ferrierite is a crystalline aluminosilicate that has been found useful as an adsorbent, catalyst or catalyst support. The syntheses of ferrierite and ferrierite-type materials such as ZSM-35 are well known. See Journal of Catalysis, Vol. 35, 256-272 (1974) and U.S. Pat. Nos. 3,933,974; 3,966,883; 3,992,466; 4,016,245; 4,088,739; 4,107,195 and 4,251,499, among others.
Ferrierite can be prepared by heating aqueous mixtures of alkali and/or alkaline earth metal, alumina and silica. See U.S. Pat. Nos. 3,933,974, 3,966,883; 4,017,590 and 4,088,739.
These synthesis methods have several disadvantages. Typically, these synthesis methods require long periods of time and require elevated temperatures for synthesis. The high temperatures that promote crystallization require pressure vessels. The SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio of the product is relatively low, usually less than about 30 and the products exhibit surface areas of less than 350 m.sup.2 /g.
The use of organonitrogen compounds commonly called templates partially overcomes some of these difficulties. Shorter crystallization times and lower synthesis temperature result from using a variety of such templates. See U.S. Pat. Nos. 4,000,248; 4,107,195; 4,251,499; and 4,795,623, among others. Even these methods do not provide ferrierite of high SiO.sub.2 /Al.sub.2 O.sub.3 ratio and purity that is desirable for many catalytic uses.
Many of the organic nitrogen compounds suggested as templates are expensive and are difficult to store and use. Many organic nitrogen compounds used in ferrierite synthesis have pKa values between 7-12 such as those disclosed in U.S. Pat. No. 4,205,053. Pyridine which has a pKa of 5.29 (See "Introduction to Organic Chemistry" by Andrew Streitweiser and Clayton H. Heathcock, published by Macmillan, New York, 1976). The use of pyridine in zeolite synthesis appears to be somewhat complicated. For example, U.S. Pat. No. 4,797,266 indicates that a preparation involving pyridine provides a mixture of zeolite ZSM-5 and ferrierite. U.S. Pat. No. 4,613,488 indicates use of pyridine or a derivative results in a novel aluminum silicate not ferrierite. U.S. Pat. No. 4,578,259 discloses the formation of "ISI-6" (an isotypic framework of ferrierite, See the Atlas of Zeolite Structure Types, by W. M. Meier and D. H. Olson, published by Butterworths-Heinemann, third revised edition, 1992, page 98) with the use of pyridine and "non-pyridine" nitrogen containing compounds or with pyridine and an oxygen containing compounds. According to U.S. Pat. No. 4,578,259, the use of pyridine alone does not result in the formation of ferrierite.
U.S. Pat. No. 4,251,499 teaches the use of piperidine and alkyl-substituted piperidines as a template. As a comparative example, the use of pyridine as a template in example 12 led to a product which contained 50% ferrierite, 30% other zeolitic material and 20% amorphous material.
EP-501,577-A1 relates to using a ferrierite catalyst in an olefin isomerization process. In example 2, it discloses a ferrierite catalyst having a molar silica to alumina of 72:1 prepared from a reaction gel with a molar composition of 93.5 SiO.sub.2 /1.0 Al.sub.2 O.sub.3 /7.4 Na.sub.2 O/19.6 Na.sub.2 SO.sub.4 /30.0 pyridine/1938 H.sub.2 O. In this example, the molar OH.sup.- /SiO.sub.2 ratio in the reaction gel was 0.16.
EP-523,838-A2 relates to using a ferrierite catalyst in an olefin isomerization process. In example 4, a ferrierite catalyst with a molar silica to alumina ratio of 87:1 having a surface area of 326 m.sup.2 /g is disclosed.
It is an object of this invention to provide a process for the preparation of highly pure high molar silica to alumina ratio ferrierites having high surface areas which exhibit excellent catalytic performance when used in skeletal olefin isomerization.